ne memorable scene in Derek Jarman's film ''Caravaggio'' shows the painter struggling for inspiration as he composes his masterpiece, ''The Marytrdom of St. Matthew'': models and hangers-on fill an improbably large studio while Caravaggio barks orders like a film director. It is a clever if simplistic metaphor of artistic creation, reflecting the criticisms leveled at the painter during his life, for Caravaggio was commonly held to paint only what he saw, invoking nature as his guide. Like all cliches, Jarman's interpretation contained a nugget of truth: Caravaggio did undermine the conventional hierarchies of art, glorying in an earthy naturalism too strong for his politer contemporaries. Yet this rebel was also courted by connoisseurs and prelates; he hungered after the status of a gentleman and was as much concerned with his rapier as his brush. Dead at 39, Caravaggio transformed painting while losing himself in a legend even more outlandish than his own life.

Helen Langdon's ''Caravaggio: A Life'' disinters the man and artist from romantic fantasies spun around him and retells his stormy career from impoverished obscurity to celebrated notoriety. Her readings of his paintings are informed by an intimate knowledge of the period; deftly interweaving artifact and milieu, she re-creates the demimonde so lovingly depicted by him and reaffirms his achievement by placing it in a new and more objective context. Hers is a familiar though risky strategy, if only because what is known of Caravaggio's life would scarcely fill a dozen pages, and her book is occasionally overwhelmed by extended discussions of prostitution or Counter-Reformation piety. Yet, given such a tale of gambling, murder and flight, no one could seriously complain. Langdon's narrative reads like a chapter from Manzoni's classic novel, ''The Betrothed,'' depicting a society in which violence was never far from the surface.

Caravaggio, who was born in 1571, first learned his craft in provincial Lombardy among artists struggling to convey naturalism and directness at a time when Rome and Florence were dominated by artistic fashions more idealized and self-referential. His training proved a saving grace when he reached Rome in 1592; he brought to his work a talent for simplicity and close observation that contrasted with the high art of the day. He later said a still life required as much skill as figurative painting, and his work was often so vivid as to make critics believe he always had a model before him. An early painting of the penitent Mary Magdalene seemed so lifelike that it was once believed to have been a simple study of a girl drying her hair, only retrospectively dignified with a religious title. Under the patronage of the influential Francesco Maria Cardinal Del Monte, Caravaggio experimented with highly colored genre paintings of cardsharps, musicians and gypsies, works that reminded contemporaries of the Venetian painter Giorgione.

When given the opportunity to demonstrate his skill on a larger scale, Caravaggio elevated the commonplace through his revolutionary canvases on the life of St. Matthew. Rejecting the ideal art of Raphael and Michelangelo, he placed the saint among the tricksters and rogues of his own day, even displacing Christ to the far corner of the canvas. A hard, cold light streams down on Matthew and renders his conversion all the more powerful by his isolation among the indifferent crowd. As Langdon reminds us, Caravaggio created a highly personal view of biblical times, couched in the fashions of contemporary Rome, thus transforming the present into an echo of biblical truth and simultaneously opening a debate about the role of naturalism in history painting.

The St. Matthew cycle brought him success, which proved as difficult to handle as failure. A subsequent altarpiece of the death of the Virgin was rejected as lascivious and shocking, for his model was reputed to be ''a dirty old whore'' from the Roman slums. Caravaggio's ''deviant'' art was matched by mood swings and violence, and in one sense his early biographers were right when they drew an analogy between his somber paintings and his character. Contemporaries observed that he was ''proud and satirical . . . always ready to argue or fight''; he brawled with allies and adversaries alike. As major commissions began to elude him, his life spiraled out of control. Finally he killed Ranuccio Tomassoni, a longtime adversary, during a murky street fight. Not lingering for justice, Caravaggio fled Rome and began a four-year exile, during which, as a later biographer wrote, ''fear haunted him from place to place.'' His last years were spent on the run in Naples, Malta and Sicily, where he produced a clutch of masterpieces whose themes dealt with persecution and death -- an extension, perhaps, of his troubled state of mind. His late painting ''The Resurrection of Lazarus,'' in Messina, seems like a reprise of his earlier altarpieces, pared to bleak essentials and with its protagonists caught in a harrowing struggle between light and dark.

It is often said every painting is a portrait of the artist, but the image of Caravaggio found in the extended essay by Leo Bersani and Ulysse Dutoit seems far removed from Langdon's biographic study. The authors are professors of French literature and film studies respectively, and their approach is fashionably interdisciplinary. In particular, they focus on the ambiguity of Caravaggio's paintings, specifically the way in which they establish a visual field that ''more or less urgently solicits and resists its own symbolization.'' As they see it, Caravaggio's paintings tap into the unconscious world of signs, where antagonism between the self and the world is acted out; they are experiments in something the authors term ''relationality.'' Their prose is typical of a certain type of academic discourse; it seems to be addressed only to true believers.

The model for ''Caravaggio's Secrets'' is the kind of semiotic study conventionally applied to intellectual cross-currents of 20th-century art. Freudian theories of the unconscious or well-worn concepts like ''the gaze'' may function with an artist like Duchamp; yet when adapted to the art of Caravaggio, this technique turns his paintings into the equivalent of movie stills, with anachronistic readings an inevitable side effect. When discussing the early ''Fortune Teller'' and ''The Calling of St. Matthew,'' the authors dwell upon the importance of ''fixed gazes -- not only the gaze of the one being seduced, but also the gaze of the seducer, who is himself (or herself) seeking in the curious and subjugated look of the other the secret of his (or her) own seductive power.'' But gazes often miss in Caravaggio, and in both these cases it is the gesture of hands that carries the dramatic burden.

One inadvertent misreading comes in the discussion of a great religious painting, ''The Conversion of St. Paul.'' Bersani and Dutoit see no working of the supernatural in this depiction of the apostle thrown from his horse by a vision. In their account, the saint reaches not toward the divine but the horse's body: ''Paul 'turns toward' a new relatedness, but one without transcendence, a relatedness with the natural nonhuman.'' A photograph of the painting may give the impression Paul is directly under his horse, but the spatial construct is more complex. The painting was designed for a side wall of a small chapel and was meant to be scanned laterally. Paul has, in fact, fallen away from his horse and he reaches out toward the heavenly light as testimony of his vision. The painting builds on contrasts of light and darkness, perception and blindness. The juxtaposition of the unseeing horse and attendant with the blind but enlightened saint goes to the heart of Paul's conversion. As often in Caravaggio, light is a metaphor for redemption and a symbol of the supernatural.

Caravaggio's modernity is as troubling today as it was 400 years ago. The power of his naturalism both celebrated art and exploited its ambiguity: genre scenes could become religious while religious art came down to the quiddity of contemporary life. His themes resonated with both the illiterate and the educated of his day, but to understand them now requires more historic than psychoanalytic analysis. To unlock his secrets, most readers will wish to turn to Helen Langdon's admirable book.

Bruce Boucher's most recent books are ''Andrea Palladio: The Architect in His Time'' and ''Italian Baroque Sculpture.''